A pyroelectric sensor is a type of thermal sensors that uses a pyroelectric element that is polarized by infrared ray emitted from a heat source such as a human body. There is known a technique of mounting a pyroelectric sensor on an electronic device so that the electronic device automatically operates based on detection of presence/absence of a human such as a user of the electronic device.
Practical examples of the pyroelectric sensor include illumination in a bathroom or the like. The usage of the pyroelectric sensor in this example is as follows. In a normal state where no human is present, the pyroelectric sensor is energized so that the pyroelectric sensor enters a standby state, during which illumination is extinguished. When a human approaches the pyroelectric sensor, an electromotive force occurs at the pyroelectric sensor, whereby the illumination is lit. If the pyroelectric sensor does not detect a human in a subsequent certain period, the illumination is extinguished and the pyroelectric sensor returns to the standby state.
Further, Patent Literature 1 discloses a display apparatus. The display apparatus can reduce power consumption during standby, by controlling lighting/extinguishing of a display element that is used for displaying time points or channels in a recorder recording television programs or the like. The display apparatus of Patent Literature 1 uses a pyroelectric sensor and a timer. Upon detection of a user by the pyroelectric sensor, the display element and the timer are turned on. After the timer has measured a predetermined time, the display element is turned off.
With illumination or a display apparatus including a pyroelectric sensor such as the one described above, automatic lighting can improve the convenience of the user. Further, automatic extinguishing can achieve power saving.